Ink jet printing refers to a method of forming type characters on a paper by ejecting ink droplets from a printhead from one or more nozzles. Several schemes are utilized to control the deposition of the ink droplets on the printing substrate or recording sheet to form the desired characters. For example, one method comprises deflecting electrically-charged droplets by electrostatic means. Another method comprises the ejection of single droplets under the control of a piezoelectric device. One type of ink employed is the so-called non-drying type which functions by quickly penetrating the substrate, e.g., paper fibers, thus giving the appearance of being dry to the touch even though still possessing a quantity of relatively low vapor pressure solvent. Another widely used type of ink are aqueous inks, that is, inks which are composed of a relatively large quantity of water which functions as the solvent and carrier for the dyes therein. Aqueous inks, however, suffer from the deficiency of lack of stability to moisture, i.e., poor water-resistance on the printed substrate which causes loss of resolution in the image. This can occur even when the printed records are stored in areas of relatively high humidity.
The image generated by an ink jet printing device may be either in the form of a reflection print wherein the image is deposited on a substantially opaque reflective substrate, for example, when the image is formed on a sheet such a paper or may comprise a transparency, that is, when the image is formed on a substantially transparent recording substrate and is viewed by illuminating the side of the substrate opposite the image side and viewing from the image side. Such material is, of course, particularly advantageous for use in viewing by projection.
Since projection of a transparency generally involves enlarging of the image, it will be seen that the image quality requirements are more stringent for a transparency than for an image viewed by reflection. Of course a transparency must take into consideration the other problems which may be common to both the transparency and to the reflection image, for example, the water fastness problem discussed above when aqueous inks are employed.
U.S. Pat. No. 4,269,981 issued May 26, 1981 is directed to a recording sheet for ink jet recording which can be viewed under both reflected and transmitted light and which comprises a support and an ink-absorbing layer provided on said support wherein said ink absorbing layer comprises a white pigment having ink-absorbing abilities and a binder resin possessing film-forming ability. As examples of suitable white pigments, mention is made of clay, talc, diatomacious earth, calcium carbonate, titanium dioxide and the like. As examples of suitable binder materials, mention is made of oxidized starch, etherified starch, gelatin, casein, hydroxyethyl cellulose, polyvinyl alcohol and the like.
See also Japanese Pat. No. 5614583 and German Pat. No. 3,024,205 for other disclosures of polyvinyl alcohol as a binder for pigments, such as calcium carbonate or micropowders such as silicic acid.
Generally, when used alone, a layer of polyvinyl alcohol is not suitable as a receptor layer for ink jet recording systems employing aqueous based inks. Such layers are often too tacky after receiving the ink.